The use of display screens as an interface between users and electronic systems of various types is attractive to the data processing industry because of its flexibility and speed. Selection of an item from the display by the user can cause a wide variety of responses by the system. It can initiate internal activities within the system, such as is involved in calling up or processing databases, or it can produce external actions, such as handling of process control functions. Further, the system can reconfigure the display presented to offer a subset of selections in response to the first selection, it can simulate cause and effect relationships, such as by simulating arrays of buttons, lights, knobs, etc., that a user might expect to encounter in a physical implementation of the display, and thereafter visualizing simulated effects of operating those elements.
In many cases, the display-to-user interface is obtained by displaying multiple items for selection on the face of a CRT, or the like, with the user employing a keyboard as the means for selecting the desired item. Typically, the selection is accomplished by entering a letter or symbol from the keyboard, or by manipulating a cursor to align with the desired selection. Other means, such as the so-called mouse and tablet devices, are also sometimes used in conjunction with cursor-oriented selection. Regardless, parallax offsetting of the displayed items or areas, as seen by the user, are irrelevant under those circumstances.
Arrangements of touch-sensitive screens or panels as an overlay to the display surface have evolved and enjoy the benefit of freeing the user from the keyboard. The elements and operation of a contemporary touch screen system are succinctly described in the article entitled COMPUTER INTERFACE DEVICE by P. J. Kennedy in the January 1980 IBM TECHNICAL DISCLOSURE BULLETIN (Vol. 22, No. 8B) at pages 3542-3543. The ease with which a user can learn to utilize such configurations is evidenced by the fact that touch screen systems have found use as training aids for small children who cannot read, much less use a keyboard. The user need only point a finger, light pen, rod, or the like, directly on the item or area seen on the screen; the controls associated with the touch screen interpret the item or area selected in a manner transparent to the user.
Unfortunately, the thickness of the face of the CRT and the touch screen intervene between the display plane and the viewer. Thus, if the user is looking along a line that is not substantially perpendicular to the plane of the target item or area for which selection is intended while little or no space separates that target from its neighbors, the user's finger or pen may well actually overlie the neighbor. The electronics will then cause erroneous selection of the neighbor.
The existence of the hazard of parallax induced pointing errors in touch screen selection is known in the prior art. For instance, U.S. Pat. No. 4,567,480 by Blanchard, as well as the January 1984 DATAMATION magazine article at pages 146-154, both recognize the problem, but neither suggests a solution other than to admonish the user to sit directly in front of the screen and at eye level.
Others have recognized the problem and tried resolution by modifying the structure associated with the touch screen. For example, U.S. Pat. No. 4,198,623 by Misek et al configures a special array of light sources and sensors in an effort to minimize the parallax effects of the edge curvature in CRT's. U.S. Pat. No. 4,355,202 by DeCosta et al teaches a frame of force translating cones and piezoelectric sensors surrounding a display in an effort to place the display and selection planes as near coincidence as possible while admitting that a finite thickness between those two planes will involve parallax distortion.
Since CRT faces have a finite thickness with the display plane occurring on the interior surface thereof, it is impossible to obtain complete coincidence between the touch screen plane and the display plane. Yet another approach is taken in U.S. Pat. No. 4,361,725 by Dagnelie et al which suggests that it is possible to arrange X-Y grid wires across the tube face in a configuration that will correct for parallax errors.
None of the known prior art has taught or suggested elimination or minimization of parallax induced touch screen selection errors in a manner that can accommodate existing touch screen panels without modifying the display, the touch screen panel, the display-to-panel mounting environment, or some combination thereof. However, that result is advantageously realized by the present invention.